Nepenthes alata Manuel Blanco, 1837
This species is from the Philippines archipelago. Originally named from samples taken from Vintars in what is now Ilocos Norte region on the island of Luzon. There is still some confusion regarding this species because the type specimen the author based N. alata on has not been found. The Manila Herbarium was destroyed during WWII; but there is a chance the specimen was deposited in the Madrid herbarium before WWII. Having access to the type is very important toward being able to make a 100% certain identification, especially when the description is too generalized and there were no illustrations.
In 1927 Danser published his monograph of Nepenthes, he did a wonderful job, but N. alata was probably his largest failure. During his study of the type specimens, he united a specimen of N. alba (this species was in turn mistakenly united with N. gracillima), N. blancoi, N. copelandii, N. eustachya and N. philippinensis (which includes N. brachycarpa) all into his concept of N. alata. These five species have since been studied in greater detail and only N. copelandii seems like it could even be a somewhat distant relative to N. alata as there are still a number of significant differences between them. Danser also included N. melamphora but the name actually refers back to specimen of N. gymnamphora from Java and so this name should not be applied to any Nepenthes from the Philippines--unless it can be shown that (A) N. melamphora isn't N. gymnamphora and (B) it is also present in the Philippines which seems highly unlikely.
There are also some other taxa Danser included into N. alata that needs to be reviewed again: N. alata var. biflora and N. graciliflora. There is a good possibility these two also represent species different from N. alata. And finally, N. alata var. ecristata appears to be a valid entity from Mindanao Island, a version of the hairless N. alata which doesn't have one of diagnostic features of the species, the basal lid keel.
It seems we are now down to two different species level taxa, but only one of which is likely to be true N. alata: A hairless plant which is widespread throughout the Philippines archipelago, from sea level and up into lower highlands. Some examples do strongly resemble N. eustachya. The upper pitchers of this species have wings with elements only near the pitcher opening. The wings are reduced to ridges on swollen base. Or the hairy plant with flatter peristomes which is positively only known from strictly highland areas on Luzon and Negros Islands. In this species the upper pitchers have wings with elements which run the entire length of the pitchers. It never resembles N. eustachya. Jebb and Cheek's version of N. alata seems to be a combination of these two taxa...
This photograph belong to Gary Kong. It shows a pitcher of the hairy, highland variety from Luzon Island. Originally from Malesiana Tropicals via Dangerous Plants.